Exercise helps maintain lost weight, and some of the effect of exercise may be additional to the calories burned with exercise. Part of this extra effect of the addition of exercise to a weight loss regimen may be by altering how skeletal muscle uses fat. Following exercise training after weight loss, more fat may go to the muscle. Also, this fat may be used in a less efficient way by the muscle, thus helping to maintain the lost weight. This study looks at how the metabolism of fat changes in the muscle following weight loss and then a period of exercise or no exercise. In general, people are only able to lose about 10% of their starting weight and then plateau. It is not known why people undergo this plateau and what factors will predict the ability to lose more weight. Due to the above described changes in fat metabolism by the muscle, it is hypothesized that after chronic exercise training , trained subjects will lose significantly more weight with a subsequent period of caloric restriction compared to subjects who have not undergone exercise training.